1. Field of the Invention
This invention relates to a belt type continuously variable transmission for a straddle type vehicle.
2. Description of Related Art
Straddle type vehicles having a belt type continuously variable transmission are known. The belt type continuously variable transmission has a primary sheave to which driving force from an engine is transmitted and a secondary sheave to which driving force is transmitted from the primary sheave via a V-belt. A speed reduction ratio varies in accordance with changes of a winding radius of the belt in the primary sheave and a winding radius of the V-belt in the secondary sheave.
If the V-belt is made of rubber, it is likely to wear and have reduced durability. Also, the V-belt may also deteriorate due to heat generation following deformation of the V-belt. Therefore, a resin block belt made of coupled multiple resin blocks has been proposed (see JP-A-2002-147553).
In a belt type continuously variable transmission having a resin block belt, the belt itself hardly wears. However another problem arises in that surfaces of the sheaves are likely to wear. Thus, JP-A-2002-147553 page 2, right column, lines 34-38) proposes plating surfaces of the primary and secondary sheaves with chrome.
The resin block belt has some extent of strength. However, it has been discovered that, if surfaces of the primary and secondary sheaves are plated with chrome, wear of the resin block belt increases. Thus, it is difficult according to the conventional art to compatibly prevent both wear of the V-belt and wear of the sheaves.